According to Nelson’s SuSy article, the big advantage of SuSy is the cancellation of distortion and noise.
I still like to fiddle with the circuit and this afternoon I connected my scope to both + and – out of my AlephX.
I put the scope in substraction mode so I could see the cancellation effect. I made sure the scope was well calibrated because the slightest mismatch gives a non-ideal figure.
I assume that this approach is the correct one to see the cancellation effect. If not, don't read any further.
Ideally there would be a flat trace, meaning the effect of SuSy is optimal. However it wasn’t the case.
Finetuning one channel of the scope’s vertical amplifier I could further improve the trace till it was really flat, no signal showed up anymore, meaning that the X-effect of the Amp can be optimised.
Now, what could be done, apart from matching all the parts as good as possible to improve SuSy?
I know we shouldn’t use servos or other non- esthetical stuff in nice X-amps, but are there simple circuits possible that measure the SuSy effect and then compensate the slight mismatches of the circuit? Or is SuSy by nature self-compensating?

I'm certainly not claiming that my AlephX is build like a factory one.
However, the P-P soldered board is fairly symmetrical,
mosfets well matched, wire about all the same length, bias at both sides equal and so on.
The main concern was if it is possible to measure the asymmetry and do something about it electronically with some simple components. A SuperSymmetry comparator or something like that.
Not being a designer, I wouldn't know where to start. I thought the idea wasn't a bad one, hence this thread.
I would like to find out if some of you have “been there and done that”.

Petter
I bought 50 IRFP240’s and measured them all with the method proposed at Passdiy.
Then I took two pairs of 16 devices with the closest match to each other.
The middle 8 ones were used for the gain devices, the 2 X 4 outer ones for the current sources.
Your approach will probably give a better result.
Don’t get me wrong, I’m not complaining about my amps, the sole purpose of this thread is to know if it is possible to measure the SuSy effect electronically and within the amp and compensate for slight mismatches.
Some kind of “Constant Active SuSy Source”

Bernard
I’m still not sure that what I did with the scope and the result of my measurements where what I thought they were.
Let me explain. Every decent scope has two channels. If you’re lucky the signal from the second channel can be inverted. That means if you put two signals into the scope, in channel A the non-inverted and in Channel B the inverted signal, (+Out and –Out of the amp) and you switch the scope to the ‘add’ function, both signals will be added to each other.
If you push the invert button from channel B, both signals will be substracted from each other. Ideally when both parts of your amps (and AlephX’s are bridged amps and thus have two parts) are behaving identical, you should see nothing but a straight line on the scope.
The SuSy topology pushes the whole process a magnitude of 100:1 further according to Nelson’s article .
The whole point of my thinking is that when I substracted the two channels the line was not straight but I could see remains of asymmetry from both halves of the amp. We’re talking µV, perhaps mV here. Not a big deal.
Still, I wonder what I saw. Was it the ‘SuSy filtered’ remains of the good signal and thus the asymmetry of both halves or did I see the distortion of the amp.
If it was the SuSy-filtered signal then both halves should be better matched, if it was the distortion, could there be a way to make the SuSy effect smarter?

Surely an X-circuit can’t make an undistorted signal out of a distorted one. The X only cancels distortion generated by both halves of the amps.

Every signal amplified and distorted by the amp itself is cancelled by SuSy around the balanced circuit (output stages , active current sources ) . The differential pair get simple cancellation from matching .